Presentation on theme: "Self-Centering Steel Frame Systems"— Presentation transcript:
1 Self-Centering Steel Frame Systems NEESR-SG: Self-Centering Damage-Free Seismic-Resistant Steel Frame SystemsProject TeamRichard Sause, James Ricles, David Roke,Choung-Yeol Seo, Michael Wolski, Geoff MadrazoATLSS Center, Lehigh UniversityMaria Garlock, Erik VanMarcke, Li-Shiuan PehPrinceton UniversityJudy LiuPurdue UniversityKeh-Chyuan TsaiNCREE, National Taiwan University
2 Current NEESR Project NEESR-SG: Self-Centering Damage-Free Seismic-Resistant Steel Frame Systems This material is based on work supported by the National Science Foundation, Award No. CMS , in the George E. Brown, Jr. Network for Earthquake Engineering Simulation Research (NEESR) program, and Award No. CMS NEES Consortium Operation.
3 Motivation: Expected Damage for Conventional Steel Frames Conventional Moment Resisting Frame SystemThe motivation for our project is the expected performance of conventional steel frames, which as is well-documented, will experience some damage under the design level earthquake, perhaps like this upper photo, even when they perform as intended. Our goal is to develop steel frame systems without such damage under the design earthqake.Reduced beam section (RBS) beam-column test specimen with slab: (a) at 3% drift, (b) at 4% drift.
4 Self Centering (SC) Seismic-Resistant System Concepts Discrete structural members are post-tensioned to pre-compress joints.Gap opening at joints at selected earthquake load levels provides softening of lateral force-drift behavior without damage to members.PT forces close joints and permanent lateral drift is avoided.MThe systems we are developing use the following concepts that we initially applied to precast shear walls about 10 years ago:
5 Previous Work on SC Steel Moment Resisting (MRF) Connections W24x62 (Fy 248 MPa),or W36x150 (Fy 350 MPa)W14x311, W14x398 (Fy 350 MPa)or CFT406x406x13 (Fy 345 MPa)PT Strands3660 to4120 mmCurrent project is built upon some previous work at Lehigh on SC steel MRFs with these post-tensioned connectionsMRF Subassembly with PT Connections6100 to 8540 mm
6 Initial Stiffness Is Similar to Stiffness of Conventional Systems DHPT Steel MRFStiffness with welded connectionMRF subassembly with post-tensioned connectionsThe next few slides summarize some of the observed behavior. Here you see a typical hysteresis loop from a SC system, with the self-centering behavior, the force-deformation behavior always returning to the origin. The slide shows that before decompression and gap opening, the initial stiffness is similar to that of a conventional system.
7 Lateral Force-Drift Behavior Softens Due to Gap Opening Steel MRF subassembly with post-tensioned connections and angles at 3% driftThis slide shows the gap opening behavior and the result that there is essentially no damage at 3% drift, even though there is a softening in the force-deformation behavior as shown in the previous slide.
8 Lateral Force-Drift Behavior Softens Without Significant Damage Conventional steel MRFs soften by inelastic deformation, which damages main structural members and results in residual driftSC steel MRF softens by gap opening and reduced contact area at jointsPost-Tensioned ConnectionWelded ConnectionDH
9 Energy Dissipation from Energy Dissipation (ED) Elements HSteel MRFSpecimen PC2L6x6x5/16, g/t = 4Specimen PC4L8x8x5/8, g/t = 4Steel MRF subassemblies with post-tensioned connections with different size ED elements.By using larger angles the connection is capable of developing more energy dissipation and higher strength.The stiffness after decompression is increased with a larger angle.
11 Summary of SC Seismic-Resistant Structural System Behavior Initial lateral stiffness is similar to that of conventional seismic-resistant systems.Lateral force-drift behavior softens due to gap opening at selected joints and without significant damage to main structural members.Lateral force-drift behavior softening due to gap opening controls force demands.Energy dissipation provided by energy dissipation (ED) elements, not from damage to main structural members.
12 NEESR-SG: Self-Centering Damage-Free Seismic-Resistant Steel Frame Systems Project Scope.Project Goals.Status of Selected Research Tasks.Summary.
13 NEESR-SG: SC Steel Frame Systems Project Scope Develop two SC steel frame systems:Moment-resisting frames (SC-MRFs).Concentrically-braced frames (SC-CBFs).Conduct large-scale experiments utilizing:NEES ES (RTMD facility) at Lehigh.non-NEES laboratory (Purdue).international collaborating laboratory (NCREE)Conduct analytical and design studies of prototype buildings.Develop design criteria and design procedures.
14 NEESR-SG: SC Steel Frame Systems Project Goals Overall: self-centering steel systems that are constructible, economical, and structurally damage-free under design earthquake.Specific:Fundamental knowledge of seismic behavior of SC-MRF systems and SC-CBF systems.Integrated design, analysis, and experimental research using NEES facilities.Performance-based, reliability-based seismic design procedures.
15 NEESR-SG: Self-Centering Damage-Free Seismic-Resistant Steel Frame Systems Project Scope.Project Goals.Status of Selected Research Tasks.Summary.
16 NEESR-SG: SC Steel Frame Systems Project Research Tasks Develop reliability-based seismic design and assessment procedures.Develop SC-CBF systems.Further develop SC-MRF systems.Develop energy dissipation elements for SC-MRFs and SC-CBFs.Develop sensor networks for damage monitoring and integrity assessment.Design prototype buildings.Perform nonlinear analyses of prototype buildings.Conduct large-scale laboratory tests of SC-MRFs and SC-CBFs.Collaborate on 3-D large-scale laboratory tests on SC-MRF and SC-CBF systems.
17 Task 2. Develop SC-CBF Systems: SC-CBF System Concept Rocking behavior of simple SC-CBF system.
18 More Complex SC-CBF Configurations Being Considered baseVP01P01+PgP02P02+Pcolroof
19 SC-CBF Design Criteria Column DecompressionPT YieldingSignificant Yielding of Frame MembersFailure of Frame MembersDBEMCELateral ForceRoof DriftIOCPLSMember yieldsPT steel yieldsSlide shows the overall performance goals for the system and where we expect the critical limit states to be reached.Under the design level earthquake we expect immediate occupancy. Column decompression and uplift is acceptable, but yielding of the post-tensioning is not. Beyond the DBE, PT yielding followed by significant yielding of the braves, beams, and columns (in that order) is acceptable. For the maximum considered earthquake the expected performance is still at the life safety level.Δgap
20 Current Work on SC-CBF Systems Evaluate frame configurations.Evaluate effect of energy dissipation (ED) elements.Develop and evaluate performance-based design approach.
24 Preliminary Results for SC-CBF Dynamic analysis results indicate self-centering behavior is achieved under DBE.Frame A has lower drift capacity before PT yielding than Frame B:PT steel is at column lines rather than mid-bay.Frame A also has lower drift demand.Energy dissipation helps to reduce drift demand and improve response.
25 Task 3. Further Develop SC-MRF Systems: Current Work Study of interaction between SC-MRFs and floor diaphragms by Princeton and Purdue.SC column base connections for SC-MRFs being studied by Purdue.
26 Interaction of SC-MRFs and Floor Diaphragms (Princeton) 2DgapqrDgapCollector BeamsApproach 1. Transmit inertial forces from floor diaphragm without excessive restraint of connection regions using flexible collectors.
27 Interaction of SC-MRFs and Floor Diaphragms (Purdue) Approach 2. Transmit inertial forces from floor diaphragm within one (composite) bay for each frame.
28 SC Column Base Connections for SC-MRFs (Purdue) Post-Tensioned BarsReinforcing PlateEnergy Dissipation PlateSlotted Keeper AngleBeam at Grade
29 Moment-Rotation Response at Column Base Identifying appropriate level of column base moment capacity and connection details, leading to laboratory experiments.
30 Task 4. Develop Energy Dissipation Elements for SC-MRFs SC systems have no significant energy dissipation from main structural elements:Behavior of energy dissipation elements determined SC system energy dissipation.Energy dissipation elements may be damaged during earthquake and replaced.For SC-MRFs, energy dissipation elements are located at beam-column connections.
31 Quantifying Energy Dissipation Define relative hysteretic ED ratio bEbE : Relative ED capacitybE = x 100(%)Area of yellowArea of blueFor SC systems: 0 ≤ bE ≤ 50%Target value: bE = 25%Hysteresis Loop
32 ED Element Assessment Consider several ED elements: Metallic yielding, friction, viscoelastic, elastomeric, and viscous fluid.Evaluation criteria:Behavior, force capacity versus size, constructability, and life-cycle maintenance.Friction ED elements selected for further study.
36 Test Matrix Test No. Loading Protocol qr,max (rads) Experimental Parameter1CS0.035Reduced Friction Force20.030Design Friction Force3Fillet Weld Repair4EQ0.025Response to EQ Loading50.065Effect of Bolt Bearing6Assess Column L Flex., CJP7Effect of Bolt Bearing, CJPCS: Cyclic Symmetric EQ: Chi-Chi MCE Level Earthquake Response
37 Test 2: Design Friction Force Beginning of Test 2qr = radsqr = rads
38 Test 2: Response-1.0-0.50.00.51.0-0.04-0.03-0.02-0.010.000.010.020.030.04Rotation,qr(rads)Normalized Moment, M/Mp,ntheoretical decompressionstiffnessreductionimminent gap openingM+-
39 Test 2: Comparison with Simplified Model Md + M+Ff2M-Ff2M+Ff1Axial stiffness of PTstrands & beamMd + M-Ff
40 Results for ED Elements for SC-MRFs Friction ED element:Reliable with repeatable and predictable behavior.Large force capacity in modest size.BFFD:Provides needed energy dissipation for SC-MRF connections.When anticipated connection rotation demand is exceeded, friction bolts can be designed to fail in shear without damage to other components.
41 Task 8. Conduct Large-Scale Laboratory Tests Two specimens, one SC-MRF and one SC-CBF, tested at Lehigh NEES ES (RTMD facility).2/3-scale 4 story frame.Utilize hybrid test method (pseudo dynamic with analytical and laboratory substructures).Utilize real-time hybrid test method, if energy dissipation elements are rate-sensitive.
42 9. Collaborate on 3-D Large-Scale Laboratory Tests Large-scale 3-D SC steel frame system tests at NCREE in Taiwan under direction of Dr. K.C. Tsai.Interaction of SC frame systems with floor diaphragms and gravity frames will be studied.3-D tests are part of Taiwan program on SC systems.Project team is collaborating with Taiwan researchers:US-Taiwan Workshop on Self-Centering Structural Systems, June 6-7, 2005, at NCREE.2nd workshop planned for October 2006 at NCREE.
43 Summary Two types of SC steel frame systems are being developed: Moment-resisting frames (SC-MRFs).Concentrically-braced frames (SC-CBFs).Research plan includes 9 major tasks:Significant work completed on 7 tasks.Numerous conference publications available from current project.Large-scale experiments utilizing NEES ES at Lehigh are being conducted.Ongoing collaboration with NCREE in Taiwan.